The present invention relates to the art of induction heating and more particularly to an apparatus for conveying elongated workpieces through a multiturn induction heating coil.
The invention is particularly applicable for heating forging billets to a forging temperature and it will be described with reference thereto; however, the invention has broader applications and may be used in various installations for inductively heating a succession of workpieces passing through an induction heating coil.
It is common practice to inductively heat elongated workpieces, such as billets to be forged, by passing the workpieces axially through an elongated passageway surrounded by a multiturn induction heating coil. A substantial amount of effort has been devoted to arrangements for conveying the workpiece itself through the passage. The most common arrangement is to provide spaced support rails or elements extending through the passage of the heating coil and a pusher rod for pushing a line of abutting workpieces along the support rails and axially through the passage wherein they are heated by energizing the induction heating coil. Several prior patents show this feature; however, one representative patent of this concept is Armstrong U.S. Pat. No. 3,057,986 which is incorporated by reference herein as background information. This pusher rod concept requires contact between adjacent workpieces moving and pushing one another through the central passage. This contact can cause certain difficulty with respect to uneven heating at the abutting surfaces between adjacent workpieces, in particular, by the contacting and cooling of the rearward end of a workpiece being heated in the heating coil by a cold workpiece being initially fed into the coil. The abutting of the workpieces against one another, such as required in the prior pusher rod arrangements, also can produce the problem of adjacent workpieces sticking together.
To overcome the major disadvantages of the prior conventional pusher rod arrangements, so-called walking beam type feeder arrangements have been provided for conveying workpieces through the central passage of the multiturn induction heating coil or coils. These walking beam arrangements generally include fixed workpiece support rails in the coil passage similar to the rails along which the workpieces are pushed in the conventional pusher rod type feeder arrangements. Then, a second set of rails is provided below the support rails and extending through the coil passage. These second rails are moved in both a vertical and longitudinal direction. By moving the second set of rails vertically upward, the workpieces are lifted in unison off the support rails where they then can be moved in a forward direction in the passage by longitudinal advance movement of the transfer or second set of rails. Thereafter, the transfer rails are shifted into a downward position which then deposits the workpieces back onto the support rails passing through the coil passage. The moving or transfer rails are then retracted and the cycle is repeated. In this manner, the workpieces can be progressively moved through the passageway of the induction heating coil for heating without requiring them to be abutted against, and in contact with one another as in the prior conventional pusher rod feeder arrangements. This then eliminates the disadvantages referred to above that are created by such contacting of the workpieces with one another. Various patents such as British Pat. No. 1,021,961 and British Pat. No. 964,439 incorporated by reference herein for background information disclose forms of such walking beam type feeder arrangements. However, all these walking beam feeder arrangements include a substantial amount of mass within the heating coil that normally affects the heating of the workpieces. In addition, because they require the lifting of the workpieces off the support rails by the transfer rails, and the movement of the workpieces through the heating coil passage while thus carried by the transfer rails, these walking beam type feeder arrangements normally require considerably more power to operate than the prior conventional pusher rod feeder arrangements, thus adding to the operating cost. Also, the walking beam or movable transfer rail concept generally involves an arrangement for cooling the moving rails along with the fixed support rails. These cooled rails, besides producing undesired cooler sections on the workpiece surfaces, cause substantial difficulty in producing fluid flow through rails which are movable both vertically and longitudinally.